Polyolefin production

ABSTRACT

A metallocene compound having the general formula: CpAXMQ 1 Q 2 Cp′A′X′M′Q 1 ′Q 2 ′ wherein Cp and Cp′ are each independently a substituted or unsubstituted cyclopentadienyl moiety; M and M′ are each independently a metal chosen from Group IV B transition metals and vanadium, and coordinate to Cp and Cp′ respectively; X and X′ are each independently a substituted or unsubstituted Group VA or VIA heteroatom and coordinate to M and M″ respectively; A and A′ are bridging groups between Cp and X and between Cp′ and X′ respectively and are independently chosen from —SiR′ 2 —O—SiR′ 2 —, —Si n R′ m —, —C n R′ m — and —CR′ 2 —SiR′ 2 —CR′ 2 —SiR′ 2 —, in which each R′ is independently H or hydrocarbyl having 1 to 20 carbon atoms, n is an integer in the range 1 to 4 and m=2 n ; each Q 1 , Q 2  and Q 1 ′ and Q 2 ′ is independently a coordinating group which is hydrogen, halogen or hydrocarbyl having 1 to 20 carbon atoms and each of Q 1  and Q 1 ′ is coordinated to both M and M′.

The present application is a Divisional Application of and claimsbenefit under 35 U.S.C. 120 U.S. patent application Ser. No. 09/459,836,filed Dec. 13, 1999, entitled “Polyolefin Production,” now U.S. Pat. No.6,407,273.

The present invention relates to a metallocene catalyst component foruse in preparing isotactic polyolefins, especially polypropylenes. Theinvention further relates to a catalyst system which incorporates themetallocene catalyst component and a process for preparing suchisotactic polyolefins.

Olefins having 3 or more carbon atoms can be polymerised to produce apolymer with an isotactic stereochemical configuration. For example, inthe polymerization of propylene to form polypropylene, the isotacticstructure is typically described as having methyl groups attached to thetertiary carbon atoms of successive monomeric units on the same side ofa hypothetical plane through the main chain of the polymer. This can bedescribed using the Fischer projection formula as follows:

Another way of describing the structure is through the use of NMRspectroscopy. Bovey's NMR nomenclature for an isotactic pentad is . . .mmmm with each “m” representing a “meso” diad or successive methylgroups on the same side in the plane.

In contrast to the isotactic structure, syndiotactic polymers are thosein which the methyl groups attached to the tertiary carbon atoms ofsuccessive monomeric units in the chain lie on alternate sides of theplane of the polymer. Using the Fischer projection formula, thestructure of a syndiotactic polymer is described as follows:

In NMR nomenclature, a syndiotactic pentad is described as . . . rrrr .. . in which “r” represents a “racemic” diad with successive methylgroups on alternate sides of the plane.

In contrast to isotactic and syndiotactic polymers, an atactic polymerexhibits no regular order of repeating unit. Unlike syndiotactic orisotactic polymers, an atactic polymer is not crystalline and formsessentially a waxy product.

WO96/00734 relates to “constrained geometry” complexes which are said tobe useful as catalysts in the production of polyethylene. Some of theconstrained geometry metallocenes according to WO96/00734 have a bridgebetween the cyclopentadienyl ring and the metal which includes adivalent heteroatom ligand. These constrained geometry metallocenes arenot reported for production of polypropylenes.

In Polymer Preprints 37(2), p474 of 1996, McKnight et al report thatsome Group IV mono-cyclopentadienyl amido complexes may be used ascatalysts in the production of polypropylene but that the polymerproduct is almost completely atactic.

In contrast, the present applicants have surprisingly found thatisotactic polypropylene may be produced using constrained geometrymetallocene catalysts, especially from a novel class of dimericmetallocene compounds.

In a first aspect, the present invention provides a metallocene compoundhaving the general formula: CpAXMQ₁Q₂Cp′A′X′M′Q′₁Q′₂ wherein Cp and Cp′are each independently a substituted or unsubstituted cyclopentadienylmoiety; M and M′ are each independently a metal chosen from Group IV Btransition metals and vanadium, and coordinate to Cp and Cp′respectively; X and X′ are each independently a substituted orunsubstituted Group VA or VIA heteroatom and coordinate to M and M′respectively; A and A′ are bridging groups between Cp and X and betweenCp′ and X′ respectively and are independently chosen from—SiR′₂—O—SiR′₂—, —Si_(n)R′_(m)—, —C_(n)R′_(m)— and—CR′₂—SiR′₂—CR′₂—SiR′₂ —, in which each R′ is independently H orhydrocarbyl having 1 to 20 carbon atoms, n is an integer in the range 1to 4 and m=2n; each Q₁, Q₂ and Q₁′ and Q₂′ is independently acoordinating group which is hydrogen, halogen or hydrocarbyl having 1 to20 carbon atoms and each of Q and Q₁′ is coordinated to both M and M′.

Preferably, at least one of Cp and Cp′ is substituted.

The metallocene compound preferably has a dimeric structure andpreferably also has an active site with local C2 symmetry.

The metallocene may be used as a catalyst component for the productionof a polyolefin, especially isotactic polypropylene.

In a further aspect, the present invention provides a catalyst system oruse in preparing polyolefins which comprises (as a metallocene compoundas defined above; and (b) an aluminum- or boron-containing cocatalystcapable of activating the metallocene compound. Suitablealuminium-containing cocatalysts comprise an alumoxane, an alkylaluminium and/or a Lewis acid.

The alumoxanes usable in the process of the present invention are wellknown and preferably comprise oligomeric linear and/or cyclic alkylalumoxanes represented by the formula:

for oligomeric, linear alumoxanes and

for oligomeric, cyclic alumoxane, wherein n is 1-40, preferably 10-20, mis 3-40, preferably 3-20 and R is a C₁-C₈ alkyl group and preferablymethyl. Generally, in the preparation of alumoxanes from, for example,aluminium trimethyl and water, a mixture of linear and cyclic compoundsis obtained.

Suitable boron-containing cocatalysts may comprise a triphenylcarbeniumboronate such as tetrakis-pentafluorophenyl-borato-triphenylcarbenium asdescribed in EP-A-0427696, or those of the general formula [L′−H]⁺ [BAr₁ Ar₂ X₃ X₄]⁻ as described in EP-A-0277004 (page 6, line 30 to page 7,line 7).

The catalyst system may be employed in a solution polymerisationprocess, which is homogeneous, or a slurry process, which isheterogeneous. In a solution process, typical solvents includehydrocarbons with 4 to 7 carbon atoms such as heptane, toluene orcyclohexane. In a slurry process it is necessary to immobilise thecatalyst system on an inert support, particularly a porous solid supportsuch as talc, inorganic oxides and resinous support materials such aspolyolefin. Preferably, the support material is an inorganic oxide inits finally divided form.

Suitable inorganic oxide materials which are desirably employed inaccordance with this invention include Group 2 a, 3 a, 4 a or 4 b metaloxides such as silica, alumina and mixtures thereof. Other inorganicoxides that may be employed either alone or in combination with thesilica, or alumina are magnesia, titania, zirconia, and the like. Othersuitable support materials, however, can be employed, for example,finely divided functionalized polyolefins such as finely dividedpolyethylene.

Preferably, the support is a silica having a surface area comprisedbetween 200 and 900 m²/g and a pore volume comprised between 0.5 and 4ml/g.

The amount of alumoxane and metallocenes usefully employed in thepreparation of the solid support catalyst can vary over a wide range.Preferably the aluminium to transition metal mole ratio is in the rangebetween 1:1 and 100:1, preferably in the range 5:1 and 50:1.

The order of addition of the metallocenes and alumoxane to the supportmaterial can vary. In accordance with a preferred embodiment of thepresent invention alumoxane dissolved in a suitable inert hydrocarbonsolvent is added to the support material slurried in the same or othersuitable hydrocarbon liquid and thereafter a mixture of the metallocenecatalyst component is added to the slurry.

Preferred solvents include mineral oils and the various hydrocarbonswhich are liquid at reaction temperature and which do not react with theindividual ingredients. Illustrative examples of the useful solventsinclude the alkanes such as pentane, iso-pentane, hexane, heptane,octane and nonane; cycloalkanes such as cyclopentane and cyclohexane,and aromatics such as benzene, toluene, ethylbenzene and diethylbenzene.

Preferably the support material is slurried in toluene and themetallocene and alumoxane are dissolved in toluene prior to addition tothe support material.

Without wishing to be bound by any theory, it is possible that thedimeric metallocene compounds described above may, in use, formcorresponding monomeric compounds which act as the active catalyticspecies. Accordingly, the dimeric compounds may be precursors for activemonomeric compounds.

In a further aspect, the present invention provides a process forpreparing polyolefins, particularly isotactic polypropylenes, whichcomprises contacting the catalyst system with at least one olefin in areaction zone under polymerization conditions. The olefin is preferablypropylene.

In a further aspect, the present invention provides use of a catalystcomprising a metallocene compound for the production of isotacticpolypropylene, wherein the metallocene compound has the general formulaCpAXMQ₂, in which Cp is a cyclopentadienyl moiety substituted so thatwhen in use isotactic polypropylene is produced; M is a metal chosenfrom Group IVB transition metals and vanadium, and coordinates to Cp; Xis a substituted or unsubstituted Group VA or VIA heteroatom whichcoordinates to M; A is a bridging group between Cp and X which is chosenfrom —SiR′₂—O—SiR′₂—, —Si_(n)R′_(m)—, —C_(n)R′_(m)——CR′₂—SiR′₂—CR′₂—SiR′₂—, in which each R′ is independently H orhydrocarbyl having 1 to 20 carbon atoms, n is an integer in the range 1to 4 and m=2n; and each Q is independently hydrogen, halogen orhydrocarbyl having 1 to 20 carbon atoms. The metallocene compoundpreferably has an active site with local Cl symmetry when the activecatalyst is in the form of a monomer.

Preferably, each cyclopentadienyl moiety is a substituted orunsubstituted indenyl, more preferably a substituted or unsubstitutedbenzoindenyl. A preferred substitution position is position 2 in thecyclopentadienyl ring, the substituent of which may be hydrocarbylhaving 1 to 20 carbon atoms, such as methyl.

M is preferably Zr.

Each heteratom is preferably nitrogen, phosphorus, oxygen or sulphur soas to provide a suitable divalent ligand for constraining the geometryof the metallocene. The heteroatom is typically substituted with H,hydrocarbyl having 1 to 20 carbon atoms or silyl and is preferablynitrogen. Each A and A′ is preferably SiR′₂ wherein each R′ ispreferably methyl.

In a further aspect of the invention, there is provided use of ametallocene compound as described above wherein the metallocene compoundis formed from a dimeric metallocene compound also as described above.

The invention will now be described in further detail, by way of exampleonly, with reference to the following Examples and accompanyingdrawings, in which:

FIG. 1 shows the results of crystal structure analysis for(Me₂Si(^(t)buN)(2-MeBenzInd) ZrCl₂)₂;

FIG. 2 shows a 13C NMR spectrum of polypropylene produced in accordancewith the present invention; and

FIG. 3 shows the results of differential scanning calorimetry on thepolypropylene.

EXAMPLE 1 Preparation of the Dimer of (t-butylamido)(2-methyl-4,5-benzoinden-1-yl)-1,1-dimethylsilane ZirconiumDichloride 1.(2-methyl-4,5-benzoinden-1-yl,)-1,1-dimethylsilyl-t-butylamine

A solution of 83.2 mmol of 2-methyl-4,5-benzoindene in 150 cc ofdiethylether was added dropwise at room temperature to a solution of83.0 mmol of dichlorodimethylsilane in 100 cc of diethylether. Themixture was stirred overnight at room temperature and then transferredon a solution of 83.0 mmol of t-butylamidolithium in 300 cc ofdiethylether. After the mixture has been stirred for 8 hours, theprecipitated lithium chloride was eliminated by filtration. The solutionwas concentrated under vacuum and 250 cc of n-pentane were added to theresidue. The brown solid which precipitated after 1 hour at 20° C. wasfiltered off and dried under an oil-pump vacuum. 20.6 g (80%) of(t-butylamido)(2-methyl-4,5-benzoinden-1-yl)-1,1-dimethylsilane wereobtained.

2. Preparation of Dilithio Salt,(2-methyl-4,5-benzoinden-1-yl)-1,1-dimethylsilyl-t-butylamide

10.0 g (32.3 mmol) of(t-butylamido)(2-methyl-4,5-benzoinden-1-yl)-1-1-dimethylsilane weredissolved in 200 cc of diethylether and 40.4 cc (64.6 mmol) of 1.6 molardiethylether solution of methyllithium were added dropwise at roomtemperture. After the mixture has been stirred overnight, the solventwas removed under vacuum. The brown residue was washed several timeswith n-pentane and dried under vacuum. 11.9 g of the dilithio salt wereobtained as a brown powder.

3. Preparation of(2-methyl-4,5-benzo-inden-1-yl)-1,1-dimethylsilyl-t-butylamido ZirconiumDichloride

11.9 g of the dilithio salt was suspended in 200 cc of pentane and 7.6 g(32.6 mmol) of zirconium tetrachloride were added in small portions. Themixture was stirred for 10 hours at room temperature. The resultingyellow solid was filtered off, washed several times with n-pentane anddried under vacuum. The solid was suspended in 500 cc of n-hexane andheated under reflux for 1 hour. The yellow solid was then eliminated byfiltration at 50° C. and the filtrate concentrated under vacuum. 1.9 g(12%) of (t-butylamido)(2-methyl-4,5-benzoinden-1-yl)-1,1-dimethylsilane zirconium dichloridewere obtained as the dimer structure determined by X-ray diffractionanalysis (yellow crystals were obtained by recrystallization indichloromethane). 1H NMR spectrum (300 MHz, CD2C12, d in ppm): 8.09-7.37(m, 7H, 2-MebenzInd-H), 2.43 (s, 3H, 2-CH3-benzInd), 1.31 (s, 9H,t-BuN), 0.87 and 0.71 (s, 3H, Me2Si).

EXAMPLE 2 Preparation of the Dimer of (t-butylamido)(2-methyl-4,5-benzoinden-1-yl)-1,1-dimethylsilane Titanium Dichloride

The procedure described in Example I was repeated with TiCl4 being usedinstead of ZrCl4.1H NMR spectrum (300 MHz, CD2C12, d in ppm): 8.08-7.32(m, 7H, 2-MebenzInd-H), 2.47 (s, 3H, 2-CH3-benzInd), 1.48 (s, 9H,t-BuN), 0.98 and 0.84 (s, 3H, Me2Si).

EXAMPLE 3 Polymerization Procedures

Each polymerization was performed in a 4 liter bench reactor with purepolypropylene or with diluent such as cyclohexane or isobutane with thequantities reported in the following Tables. Polymerisation wasinitiated by introducing metallocene (1 to 10 mg) precontacted with 1 mlof MAO (methylaluminoxane) (30% solution in toluene obtained from WITCO)three minutes prior to its introduction into the reactor.

Table 1 shows the results of polypropylene production using the catalystof Example 1 in an amount of 2.8 mg in 21 diluent with 850 ppmcocatalyst. A polymer with a high melting point is obtained in the formof a crystalline powder. 13C NMR analysis confirms that thepolypropylene is isotactic and Table 2 shows the pentad intensitydistribution thereof. A high mmmm pentad intensity of 87% is observedwith mm triads of 93% and m dyads of 95.5%. These results are comparableto those obtained with polypropylenes made using highly stereoselectivestereorigid classical metallocene based catalysts. The relatively lowoccurence of 2-1 and 1-3 regiodefects is very surprising. The highstereoregularity of the polymer explains the high melting pointobserved.

FIG. 2 shows a 13C NMR spectrum of the polymer and FIG. 3 shows a HNMRspectrum of the metallocene in CO₂Cl₂ at 25° C.

TABLE 1 Polymerization with (Me₂Si(^(t)buN) (2-MeBenzInd)ZrCl₂)₂ Pol.Melt. Temp Residence Mn Mw Mz Temp (° C.) time (mins) (Da) (Da) (Da) DD′ (° C.) 60 60 60,900 259,800 704,000 4.3 2.7 146.9 Key: MI₂ = Meltindex; Mn = number average molecular weight; Mw = weight avergemolecular weight; D = Mw/Mn; D′ = Mz/Mw

Table 2 Microtacticity with (Me₂Si(^(t)buN) (2-MeBenzInd)ZrCl₂) PENTADSSequence % mmmm 86.93 mmmr 4.94 rmmr 1.14 mmrr 3.66 rmrr + mrmm 0.64mrmr 0.60 rrrr 0.39 mrrr 0.41 mrrm 1.29 TRIADS Sequence % mm 93.01 mr4.90 rr 2.09 DYADS Sequence % m 95.46 r 4.54 Misinsertions mole % 2, 10.33 1, 3 0.00

What is claimed is:
 1. A process for preparing polyolefins, whichcomprises contacting a catalyst system comprising (a) a metallocenecompound having the general formula: CpAXMQ₁Q₂Cp′A′X′M′Q₁′Q₂′ wherein Cpand Cp′ we each independently a substituted or unsubstitutedcyclopentadienyl moiety wherein each said cyclopentadienyl moiety issubstituted or unsubstituted indenyl; M and M′ are each a metal chosenfrom Group IV B transition metals and vanadium, and coordinate to Cp andCp′ respectively; X and X′ are each independently a substituted orunsubstituted Group VA or VIA heteroatom and coordinate to M and M′respectively; A and A′ are bridging groups between Cp and X and betweenCp′ and X′ respectively and are independently chosen from—SiR′₂—O—SiR′₂—Si_(n)R′_(m)—, —C_(n)R′_(m)— and —CR′₂′SiR′₂—CR′₂—SiR′₂—, in which each R′ is independently H or hydrocarbylhaving 1 to 20 carbon atoms, n is an integer in the range 1 to 4 andm=2n; each Q₁, Q₂ and Q₁′ and Q₂′ is independently a coordinating groupwhich is hydrogen, halogen, or hydrocarbyl having 1 to 20 carbon atomsand each of Q₁ and Q₁′ is coordinated to both M and M′; and (b) analuminum- or boron-containing cocatalyst capable of activating themetallocene compound with at least one olefin in a reaction zone underpolymerization conditions.
 2. A process according to claim 1, whereinthe olefin is propylene and the polyolefin is isotactic polypropylene.3. A process according to claim 1, wherein the metallocene compound is(t-butylamido) (2-methyl-4,5-benzoinden-1-yl)-1,1-dimethyl silanezirconium chloride or (t-butylamido)(2-methyl-4,5-benzoinden-1-yl)-1,1-dimethyl silane titanium chloride. 4.A process according to claim 1 wherein said metallocene compound has anactive site and wherein said active site has local C2 symmetry.
 5. Aprocess according to claim 1 wherein the indenyl moiety is benzoindenyl.6. A process according to claim 1 wherein the cyclopentadienyl moiety issubstituted at position 2 with a hydrocarbyl having 1 to 20 carbonatoms.
 7. A process according to claim 1 wherein said metallocenecompound has a dimeric structure.
 8. A process according to claim 1,wherein the metal is Zr.
 9. A process according to claim 1, wherein theheteroatom is nitrogen, phosphorus, oxygen or sulphur and is substitutedwith H, hydrocarbyl having 1 to 20 carbon atoms or silyl.
 10. A processaccording to claim 9, wherein the heteroatom is nitrogen.
 11. A processaccording to claim 1 wherein A is SiR′₂.
 12. A process according toclaim 11, wherein each R′ is methyl.
 13. A process according to claim 1,wherein the catalyst further comprises an aluminum- or boron-containingcocatalyst capable of activating the metallocene compound.
 14. A processaccording to claim 1, wherein the catalyst system further comprises aninert support present application is a Divisional.